Like a commenter on Reddit stated, none of the many articles about this say anything about the horse wanting the costume to stay on. At best, the horse just didn't care.
Okay I call bullshit. I have worked with 1000+ horses and not one of them liked having their head covered. I have trained all my personal horses to take a blindfold. It can be an essential piece of training and can save your horse's life someday. Just because they are trained to be blindfolded doesn't mean they want to be blindfolded. Especially in some stupid box thing that covers their whole head. That also diminish smell and hearing their two primary senses.
What you see here is a very well trained draft horse(probably a Percheron). Pulling horses are much more used to weird shit hanging off them. Also they always get some level of blindfold training, because they wear blinders when they pull.
I've been around plenty of horses that were much more comfortable in their fly masks and blinders than without them. I've seen them play and just do shit that I'm pretty sure they find humorous. Horses can be weird.
Fly masks are much different than anything that is blinding. They can see through them, they don't obstruct the nose or the ears. Most horses are fine with fly masks especially when they figure out they keep the flies off. Have met some horses that really hate them regardless of how many flies.
Yeah they are definitely very funny animals. Very curious yet flighty. I find a big difference between their willingness to do something that is my idea versus their idea.
I do not train horses but am an animal and have had a few animals as pets. No one likes shit on their head. I'm glad you gave credence from an actual expert on the subject but I could smell the bullshit from this caption a mile away.